Monday, March 27, 2006

RealClimate » How much future sea level rise?

Did I not just ask this question? Real Climate weighs in with an ambivalent answer: How much future sea level rise? More evidence from models and ice sheet observations.

What does all this news mean in practice? Reading the editorials in Science, and quotations from various researchers in newspaper articles, one might be under the impression that we should now expect 'catastrophic sea-level rise' (as Science's Richard Kerr writes). Of course, what is catastrophic to the eye of a geologist may be an event taking thousands of years. In the Otto-Bliesner et al. simulations, it takes 2000-3000 years for Greenland to melt back to its LIG minimum size. And while we don't advocate sticking with the typical politician's time frame of 4 or 5 years, the new results do not require us to revise projections of sea level rise over the next century or so. This is because even with Arctic temperature continuing to rise rapidly, there will still be significant delay before the process of ice sheet melting and thinning is complete. There is uncertainty in this delay time, but this is already taken into account in IPCC uncertainty estimates. It is also important to remember that the data showing accelerating mass loss in Antarctica and rapid glacier flow in Greenland only reflect a very few years of measurements -- the GRACE satellite has only been in operation since 2002, so it provides only a snapshot of Antarctic mass changes. We don't really know whether these observations reflect the long term trend.

On the other hand, none of the new evidence points in the direction of smaller rates of sea level rise in the future, and probably nudge us closer to the upper end of the IPCC predictions. Those who have already been ignoring or naysaying those predictions now have even less of a leg to stand on. Coastal managers, real estate developers, and insurance companies, at the least, would be wise to continue to take such predictions seriously.** As Don Kennedy and Brooks Hanson write in the lead Editorial, 'accelerated glacial melting and larger changes in sea level should be looked at as probable events, not as hypothetical possibilities.'
Many years ago while arguing on-line with a bunch of global warming skeptics, I argued that one way to combat the "we just don't know" argument would be to have actuaries study the global warming risks. More and more I hear people talk about similar approaches to the problem. As climate change looms upon us, maybe it is time to shift the political discussion to an economic one. Stop the empty political rhetoric and crank up the spreadsheets. It's happening. Time to adapt.

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